The present invention is in the field of inertial measurement units of the type typically mounted on an a movable object, e.g. a marine vessel, a land vehicle or an airborne vehicle. In particular, the invention is concerned with a housing for such a unit.
The term xe2x80x9cairborne vehiclexe2x80x9d used herein in the specification and claims refers collectively to flying objects such as airplanes, missiles, rockets, etc. However, the invention is by no means restricted to any type of moving objects which are collectively referred to herein in the specification and claims as a xe2x80x9cmoving objectxe2x80x9d.
Inertial measurement units (IMU""s) are commonly mounted on moving objects, e.g. an airborne vehicle for obtaining data regarding orientation of a flying object, namely, acceleration and rotation in three main axes (pitch, yaw and role) with respect to an axis of the flying object from which it is possible to derive information such as location, attitude, etc. An IMU is part of an inertial navigating system (INS) which comprises, among others, also a processor unit.
An IMU typically comprises a set of sensors for measuring acceleration and rotation along the three main axes. For that purpose, there are provided pairs of accelerometers for measuring acceleration, and gyros for measuring rotation. The gyros may be mechanical gyroscopes suitable for measuring rotation in two axes (in which case two such gyros will suffice) or, fiber optic gyros (FOG) which measure rotation only in one axis. Alternatively, the gyros may be ring laser gyros (RLG). Three gyros of the two latter types are required for measuring rotation in the three main axes, namely yaw, role and pitch of the moving vehicle. Such rotation sensors and accelerometers are collectively referred to as xe2x80x9csolid state sensorsxe2x80x9d.
The data received from the IMU is then transferred to a suitable processor wherein it is converted into useful navigating information for guiding and controlling the moving object, so as to follow a target or according to any moving protocol, e.g. flying, diving, etc.
In order to obtain precise data, it is required that the IMU be mounted onto the body of the moving vehicle at a fixed position with predetermined reference to an axis of the moving vehicle, typically a longitudinal axis thereof. The arrangement is such that the ratio between an axis of the moving vehicle and an axis of the IMU is known, whereby suitable calculations may be carried out for obtaining correction factors. For that purpose it is important that the housing of the IMU be fitted with true position and fixing arrangement, cooperating with corresponding means fitted on the moving vehicle, and suitable arrangements for fixing the IMU in that position. Thus, since the solid state sensors are fixedly received and articulated to the housing, their orientation (respective position with respect to an axis of the airborne vehicle) is calculable.
An evergrowing concern of moving vehicle designers and in particular of airborne vehicles is to reduce the size and weight of such vehicles wherein the volume per weight factor is of great importance and has direct influence on the overall payload which the airborne vehicle may carry. Still of importance is the projection of the IMU from the body of the airborne vehicle which influences the aerodynamic performances of the moving vehicle.
It is an object of the present invention to provide a housing for an IMU, fitted with solid state sensors for measuring acceleration and rotation about three main axes, and which is considerably compact in size, weight and volume and which is suitable for mounting on a moving object.
The main object of the present invention is to provide an inertial measurement unit (IMU) for a moving vehicle, fitted with a housing accommodating three solid state sensor couples, which has a significantly lower volume and weight as well as a low projection, as compared with known such platforms.
In accordance with the present invention there is provided an inertial measurement unit mountable on a moving vehicle, said system comprising a carrying a platform accommodating three solid state sensor couples, each couple comprising a gyro member for measuring rotation and an associated accelerometer for measuring acceleration about three main axes; said housing being in the shape of a triangular pyramid, with a base thereof fitted with true position and fixation means for positioning and fixing the housing at a predetermined relation with respect to an axis of the moving vehicle; and where each of said solid state sensor couple is fitted on a respective face of the housing.
By another aspect of the present invention there is to provided a housing for an inertial measurement unit, the housing being in the shape of a truncated triangular pyramid, and where each face thereof is fitted with a solid state sensor couple, each couple comprising a gyro member and an associated accelerometer.
By a specific embodiment of the invention, the pyramid-shaped housing is a truncated triangular pyramid with the solid state sensors mounted on respective faces of the housing for measuring acceleration and rotation about three main axes orthogonal to one another, fixed with respect to an axis of the moving vehicle, and where these axes coincide.
By one particular embodiment, the moving vehicle is an airborne vehicle.